- Technical description and explained code P0740
- Symptoms of vehicle malfunctions
- Factors that can cause this error code
- How to fix or reset OBD-2 code P0740
- Diagnose and repair of problems
- Torque converter clutch solenoid (TCC)
- Transmission control module (TCM)
- On which vehicles does this problem occur most frequently
Fault code P0740 is called “Torque Converter Clutch (TCC) Circuit Malfunction” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0740
Diagnostic Code P0740 is set when the PCM or TCM detects a fault in the electronic pressure control solenoid valve circuit. Computer controlled automatic transmissions use variable hydraulic pressures to shift gears and operate the torque converter clutch (TCC).
Modern vehicles equipped with automatic transmissions use a torque converter between the engine and transmission. It is used to increase the output torque of the engine and wheel drive.
The engine and transmission are actually linked by a hydraulic clutch mechanism inside the torque converter. Which increases torque until the speeds equalize.
The torque converter clutch (TCC) solenoids, direct the hydraulic fluid and engage the torque converter clutch to create a strong connection and increase efficiency.
When the transmission solenoid is faulty, in most cases the problem is not in the electrical part. Although the P0740 error indicates just that. The problem is usually a foreign material obstructing the mechanical operation of the solenoid or the flow of fluid through the transmission valve body.
The linear pressure solenoid valve regulates the discharge pressure of the oil pump. According to driving conditions, in response to a signal sent from the Transmission Control Module (TCM) or Powertrain Control Module (PCM).
Symptoms of vehicle malfunctions
The main signal that an error P0740 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will light up (the code will be recorded in the memory as a fault).
- The vehicle enters the transmission emergency mode.
- The transmission slips when shifting gears.
- Transmission is stuck in gear.
- Hard gear shifting.
- Transmission overheating.
- Increased fuel consumption.
- Problems with engagement and disengagement of torque converter lockup clutch.
The error P0740 is quite serious, as its occurrence may cause problems with the car controllability. There may be problems with the transmission, which will affect the operation of the engine. It is recommended to eliminate it as soon as possible to prevent more serious consequences.
Factors that can cause this error code
The error code P0740 can mean that one or more of the following problems have occurred:
- The torque converter clutch solenoid valve (TCC) is defective.
- Contaminated fluid or clogged transmission filter.
- Low transmission fluid level.
- Clogged transmission fluid passages.
- Faulty transmission pump or transmission valve housing.
- Other mechanical problems inside the transmission.
- A wiring problem or damaged connector.
- In rare cases, malfunction of PCM or TCM.
How to fix or reset OBD-2 code P0740
Some suggested steps for troubleshooting and fix the error code P0740:
- Change ATF fluid and filter.
- Fill transmission fluid to required level.
- Flushing to clean internal ducts of the transmission.
- Test, if necessary replace faulty pressure control solenoid valve.
- Repair or replace faulty transmission pump and transmission valve housing.
- Check connectors as well as wiring.
- Flash or replace PCM/TCM.
Diagnose and repair of problems
Before you begin the process of troubleshooting P0740, you should research the technical service bulletins (TSB) for your particular vehicle. In some cases, this can save a lot of time by pointing you in the right direction.
Next, you should check the fluid level and check for contamination. Before replacing the fluid, you should check the vehicle’s records to see when the filter and fluid were last changed.
After that, you should do a detailed visual inspection to check the condition of the wiring for obvious defects. Check the connectors and wiring to the torque converter solenoid valve and the PCM or TCM.
Normal readings for wiring and connections should be 0 ohms of resistance. The wiring continuity check should always be done with power disconnected from the circuit. To avoid short-circuiting and creating additional damage.
Resistance or lack of continuity indicates faulty wiring that is open or shorted. This will require repair or replacement.
Torque converter clutch solenoid (TCC)
Check resistance in the TCC solenoid and transmission inner wiring after removing the wiring harness connector. The multimeter should be set to an ohm scale with positive and negative leads on the pins for the TCC power and control circuit.
The resistance should be within the manufacturer’s specifications. If it is very high or exceeded. Remove the transmission oil pan to inspect the solenoid inside the transmission, if possible. Check voltage at either the TCC solenoid supply circuit or the wiring harness connector on the TCM.
Transmission control module (TCM)
Since the torque converter clutch is activated only during certain driving conditions. It will be necessary to monitor the TCM with an advanced diagnostic tool. To determine if the TCM is sending a command to the TCC solenoid and what the actual feedback readings are.
To check if the TCM is actually sending a signal, you will need a graph multimeter set up for duty cycle or a digital storage oscilloscope. Connect the positive wire of the multimeter, to the wiring harness going to the TCM. And the negative wire to a good ground.
The duty cycle should be the same as the one set by the TCM in the extended readout of the diagnostic tool. If the cycle remains at 0% or 100% or is intermittent, check the connections again. If all wiring and solenoid are OK, but error P0740 remains, the TCM may be defective.
On which vehicles does this problem occur most frequently
Fault code P0740 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Acura (MDX, TL)
- BMW (E39, E46)
- Chevrolet (Avalanche, TrailBlazer)
- Chrysler (Town and Country, Voyager)
- Dodge (Caravan, RAM, Stratus)
- Honda (Accord, Odyssey)
- Hyundai (Santa Fe)
- Jeep (Grand Cherokee)
- Kia (Sorento, Spectra, Sportage)
- Mitsubishi (Eclipse, L200, Montero, Outlander, Pajero)
- Nissan (Murano, Pathfinder, Tiida, X-Trail)
- Subaru (Legacy, Outback)
- Volkswagen (Bora, Golf, Jetta)
Fault code P0740 can sometimes be found with other errors. The most common are the following: P0130, P0400, P0700, P0716, P0721, P0730, P0741, P0742, P0743, P0744, P0753, P0758, P0761, P0775, P0779, P0780, P0785, P0791, P0963, P0967, P1217, P1687, P1739, P1810, P2769, P2770, P2815.